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Class definitions form the foundation for Java OOP. They are discussed in increasing detail in subsequent modules. This module sheds just a little more light on classes.

Revised: Mon Mar 28 00:23:43 CDT 2016

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Table of contents


This module is part of a collection of modules designed to help you learn to program computers.

This module sheds a little more light on the Java construct called a class .


  • Listing 1 . General syntax for defining a Java class.


New types

Java makes extensive use of classes. When a class is defined in Java, a new type comes into being. The new type definition can then be used to instantiate (create instances of) one or more objects of that new type.

A blueprint

The class definition provides a blueprint that describes the data contained within, and the behavior of objects instantiated according to the new type.

The data

The data is contained in variables defined within the class (often called member variables, data members, attributes, fields, properties, etc. ).

The behavior

The behavior is controlled by methods defined within the class.

State and behavior

An object is said to have state and behavior . At any instant in time, the state of an object is determined by the values stored in its variables and its behavior is determined by its methods .

Class vs. instance

It is possible to define:

  • instance variables and instance methods
  • static or class variables and static or class methods.

Instance variables and instance methods can only be accessed through an object instantiated from the class. They belong to the individual objects, (which is why they are called instance variables and instance methods) .

Class variables and class methods can be accessed without first instantiating an object. They are shared among all of the objectsinstantiated from the class and are even accessible in the total absence of an object of the class.

The class name alone is sufficient for accessing class variables and class methods by joining the name of the class to the name of the variable or method using a period.

Defining a class in Java

The general syntax for defining a class in Java is shown in Listing 1 .

Listing 1 . General syntax for defining a Java class.
class MyClassName{ . . .} //End of class definition.

This syntax defines a class and creates a new type named MyClassName .

The definitions of variables, methods, constructors, and a variety of other members are inserted between the opening and closing curly brackets.


This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Jb0170: Java OOP: A little more information about classes.
  • File: Jb0170.htm
  • Originally published: 1997

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.

Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.


Questions & Answers

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
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